The Facts About Income Tax Millions faithfully file their 1040 forms each April. But some things about federal income taxes may surprise you. Share | Related Content Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates. Tax Reform: Before and After What did the 2017 Tax Cuts and Jobs Act change? Here's a quick snapshot. Social Security Taxes Estimate how much of your Social Security benefit may be considered taxable.